Power lines (also known as “conductors”) are supported by power line poles, which may be wooden, metal or other typically used materials. The power lines, such as electrical transmission or distribution lines, are mounted to primary insulators. Primary insulators are typically made of a ceramic material or a synthetic polymer material and have various shapes and designs depending on the required voltage rating. The interior of the primary insulator is typically threaded in order to mate with a threaded element (also known as an “insulator thread”) in accordance with the dimensions specified by ANSI C 135.17 (1988), either for a one inch or a one and three-eighths inch thread.
The threaded element, with which the primary insulator mates, is typically formed on a pin, which is directly or indirectly mounted to the power line pole. As used herein, the term “pin” includes any conventionally used rod-like element adapted for insertion into the interior of a threaded element for a primary insulator. Known pins include brackets, spacers, attachments and the like. As disclosed in U.S. Pat. No. 5,413,443, the entire disclosure of which is hereby incorporated herein, pins are usually metal or fiberglass or fiberglass with metal ends and can be mounted at the top of a power line pole (i.e. pole-top pin) or on the side of a power line pole (i.e. side pole pin).
After mounting the primary insulator on the threaded element, the assembled unit must be resistant to rotational and tensile forces. Such forces can be caused by movement, or galloping, of the power line as a result of wind, or sudden dropping of ice or snow from the power line, or other forces. Excessive rotational forces could inadvertently be applied to the unit during installation of the primary insulator on the threaded element. Finally, the threaded element is preferably self-lubricating or easily conforming to the contour of the internal insulator thread to facilitate installation of the primary insulator on the threaded element.
To meet these needs, lead has been used in the industry as the material for the threaded element. Lead has a low melting point, is pliable and is self-lubricating. However, lead has been listed as a hazardous material by the Environmental Protection Agency and other authorities. Therefore, there is reason to avoid the use of lead as a material for the threaded element.
One such effort involves forming a threaded element with an inner diameter which increases along its length from the top to the bottom of the threaded element. Such a threaded element would have a generally constant thickness along its length because the above-mentioned ANSI specification requires that the outer diameter of the threaded element also increase along its length from top to bottom. An adhesive resinous material is placed between the inner diameter of the threaded element and the outer surface of the pin. In such a system, the point of least resistance to an upward tensile force on the primary insulator (and thus on the threaded element) is the relatively weak bond between the threaded element and the epoxy.